1. Field of the Invention
The present invention relates generally to detection protocols. More particularly, the present invention relates to detection protocols for detecting a configuration of a device connected via Ethernet connection.
2. Background Art
Power over Ethernet (also known as PoE) is a technology that allows electronic devices such as IP telephones, wireless LAN Access Points, Security network cameras and other IP-based terminals to receive power, in parallel to data, usually over an existing CAT-5 or similar Ethernet infrastructure without the need to make modifications to the infrastructure. PoE integrates data and power on the same wires and does not interfere with concurrent network operation. However implementation of PoE solutions involves numerous challenges. First and foremost, the solution must closely comply with communication and safety standards.
As PoE technology continues to advance, there is an increasing need to ensure newer technologies and protocols used within PoE devices remain compatible with conventional configurations while also offering the ability to detect when a connected device is compatible with these newer technologies and protocols, providing for a safe activation of such new communication and/or power features between connected, mutually compatible devices. This detectability should be, preferably, on the physical layer of emerging devices such that conventional power up and communication between connected devices is not required to identify a device as being compatible with a new set of protocols or features. However, because detection is required on the physical layer, devices which implement new technologies require a physical difference in the circuitry and an associated method of detection such that detection on the physical layer is possible when a detection power pulse is applied to such a device.
In a conventional PoE arrangement a power sourcing equipment device (PSE) is connected to a powered device (PD) via an Ethernet cable. FIG. 1b shows a typical Ethernet cable 130, also known as a medium-dependent interface (MDI or RJ-45), as commonly used in PoE applications. The Ethernet cable 130 serves as the data/power interface between Ethernet elements, for example between a PSE and a PD. Ethernet cable 130 includes 8 conductors arranged into 4 pairs. Conductor 1 and 2 comprise a first data pair 132, conductors 3 and 6 comprise a second data pair 134, conductors 4 and 5 comprise a first spare pair 136 and conductors 7 and 8 comprise a second spare pair 138. Each Ethernet cable 130 includes a modular connector 140 at each terminating end, thus allowing universal connection between any PSE and PD designed for use in a PoE application. Under IEEE 802.3at standard a PSE has two optional connection methods to deliver power from a PSE to a connected PD, Alternative A & B. Table 1 details the two power feeding alternatives.
TABLE 1PSE Pinout alternativesAlternative AAlternative AAlternative BConductor(MDI-X)(MDI)(All)1Negative VPSEPositive VPSE2Negative VPSEPositive VPSE3Positive VPSENegative VPSE4Positive VPSE5Positive VPSE6Positive VPSENegative VPSE7Negative VPSE8Negative VPSE
According to IEEE 802.3at standard, “Alternative A” allows power to be supplied to a PD via first and second data pairs 132,134 only, in either polarity. For example, a positive polarity applied to conductors 1, 2 of first data pair 132 and a negative polarity applied to conductors 3, 6 of second data pair 134, is “Alternative A (MDI)”. Where this same connection is made, but with polarities reversed, “Alternative A (MDI-X)” is utilized. IEEE 802.3at standard alternatively allow power to be supplied via first and second spare pairs 136,138, but in just one polarity. “Alternative B” requires that a positive polarity be applied to conductors 4, 5 of first spare pair 136 and a negative polarity be applied to conductors 7, 8 of second spare pair 138. Thus, the IEEE 802.3at standard prohibits a compliant PSE from applying power to all 4 pairs simultaneously and a compliant PD from receiving power from all 4 pairs simultaneously. Under the IEEE 802.3af standard, each conductor pair is rated to carry a maximum of approximately 15 watts. Under the IEEE 802.3at standard, each conductor pair is rated to carry a maximum of approximately 30 watts. Thus, a device which utilizes Alternative A or B, as disclosed above, to either provide or receive power may be commonly called a 2-pair or 30 watt device.
Thus, an IEEE 802.3at compliant PSE can provide power to a connected PD via first and second data pairs 132,134 in either polarity, or via first and second spare pairs 136,138 with positive polarity applied only to first spare pair 136 comprising conductors 4, 5.
Though not strictly within the ambit of the IEEE standard, there are also some devices in which power is applied via all 4 pairs, 30 W each and up to 60 W combined, but in which the rest of the IEEE standard is maintained in spirit. Thus, these 4-pair PSE devices will apply power on all 4 pairs according to Alternative A, both possibilities of either polarity, combined with power according to Alternative B or single polarity, thus utilizing all 4 pairs of the Ethernet cable. However, in accordance with the IEEE standard, in such 4-pair cases, to keep to the underlying spirit of IEEE802.3at and also for maintaining backwards compatibility, power is usually never applied in the reverse polarity of Alternative B.
FIG. 2 discloses a system 200 including a conventional PD 220. To be compatible with both Alternative A power arrangements, first and second data pairs 132,134, comprising conductors 1, 2 and 3, 6 respectively, are input to first and second input terminals of a first full-wave rectifier 222. Although not expressly required according to IEEE standards, all known or practical commercial PDs, for example PD 220, also input first and second spare pairs 136,138, comprising conductors 4, 5 and 7, 8 respectively, into a second full-wave rectifier 224. A standard IEEE signature resistor R1 having a resistance of, for example, 25 kΩ is then connected across the outputs of first and second full-wave rectifiers 222,224 such that a first terminal of resistor R1 is connected across the rectified positive rails of both first and second full-wave rectifiers 222, 224 and a second terminal of resistor R1 is connected across the rectified negative rails of both first and second full-wave rectifiers 222,224. Thus, if a reverse polarity of the Alternative B connection scheme is applied to conventional PD 220 at the spare pair inputs 136,138 such that the negative polarity is applied to second spare pair 138, comprising conductors 4, 5, the voltage across and current through signature resistor R1 of conventional PD 220 is the same as with Alternative B. Thus, conventional PD 220 cannot distinguish, on the physical layer, between a PSE which applies an IEEE compliant, Alternative B polarity power from a PSE which applies a reverse Alternative B polarity, the significance of which will become apparent when describing the present invention.
Moreover, because currents passing through first and second full-wave recitifiers 222,224 will always pass through signature resistor R1, and will pass through in the same direction, a PSE applying a detection power pulse will not be able to distinguish between different PDs, on the physical layer, based solely on application of detection voltage pulses, having particular polarities, to data pairs 132,134 and spare pairs 136,138, the significance of which will also become apparent when describing the present invention. Thus, conventional applications of PoE do not allow for the mutual detection of emerging devices having added functional capabilities, on the physical layer, such that conventional power up and communication between connected devices is not required to identify a device as being compatible with a new set of protocols or features.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a physical design and associated detection protocol that is relatively inexpensive and simple to implement but that allows backwards compatibility with older PoE devices while also offering detection of a connected device capable of utilizing these new features or protocols on the physical layer without having to blindly power up, and communicate with, the connected device to make such a determination.